1. Technical Field
This invention relates to the installation of packers in a well. Packers are seals which are placed between the casing of a well and the production tubing so that the tubing communicates only with the hydrocarbon-bearing subsurface strata. It is of course necessary to proceed with the installation or setting of these packers at the desired depth in the well.
2. Background Information
Some so-called permanent packers are placed during the first lowering. They are installed at the desired depth by an explosive or hydraulic control. They exhibit different drawbacks which make them difficult to use for drill stem testing operations before production when a perforation system carried by the drill string is used. In any case, the inner diameter available to go through the packer remains small. In a variant, these packers can be made retrievable, which does not however eliminate the drawbacks mentioned.
At the present time, for the above-mentioned testing operations, mechanically-controlled packers are used, these tools moreover being retrievable. However, the actuation of these tools requires significant rotational and translational movements of the drill string. This results in serious difficulties when it is desired to use such tools in land wells which are deviated or which exhibit slope discontinuities. Furthermore, for offshore operations, the ship or the semi-submersible drilling unit is itself subjected to non-controllable movements in relation to the sea bottom and the conventional hydraulic control lines used do not allow significant rotational movements of the drill string. In short, the movements necessary for controlling tools of this type, i.e. rotational, pulling and pushing movements on the production tubing, make them incompatible with many applications in which they would be very useful.
There are also hydraulically controlled packer devices. The control is obtained by placing the tool string under pressure. However, the application of these tools is not possible in the case of the above-mentioned testing operations for the following reasons: the tool string making up the production tubing is then lowered with a downhole valve at its lower end, the valve being closed during the lowering. With the production tubing empty or almost empty, it is practically out of the question to pressurize it. Moreover, the tests often require the incorporation, within the tool string, of pressure-sensitive devices, which are poorly suited to pressurizing within the drill string.